U.S. patent application number 14/853000 was filed with the patent office on 2016-01-07 for determining a color of a color patch.
The applicant listed for this patent is HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P.. Invention is credited to Emilio Angulo Navarro, Jordi Arnabat Benedicto, Oriol Borrell Avila, Francisco Javier Perez Gellida, Juan Uroz Soria.
Application Number | 20160001582 14/853000 |
Document ID | / |
Family ID | 48947848 |
Filed Date | 2016-01-07 |
United States Patent
Application |
20160001582 |
Kind Code |
A1 |
Arnabat Benedicto; Jordi ;
et al. |
January 7, 2016 |
DETERMINING A COLOR OF A COLOR PATCH
Abstract
A measured distance is received from a distance sensor, where
the measured distance is indicative of a distance between a color
sensor and a substrate. Using the measured distance, a location of
a given projection of projections of a substrate support is
determined. A color of a color patch on the substrate at the
determined location of the given projection is determined.
Inventors: |
Arnabat Benedicto; Jordi;
(Tarragona, ES) ; Perez Gellida; Francisco Javier;
(Barcelona, ES) ; Uroz Soria; Juan; (Terrassa,
ES) ; Borrell Avila; Oriol; (Sabadell, ES) ;
Angulo Navarro; Emilio; (Barcelona, ES) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P. |
Houston |
TX |
US |
|
|
Family ID: |
48947848 |
Appl. No.: |
14/853000 |
Filed: |
September 14, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14375554 |
Jul 30, 2014 |
9132681 |
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PCT/US2012/024090 |
Feb 7, 2012 |
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14853000 |
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Current U.S.
Class: |
347/19 |
Current CPC
Class: |
B41J 2/175 20130101;
B41J 29/393 20130101; G01J 2003/503 20130101; G01J 3/0289 20130101;
G01J 3/524 20130101; B41J 2029/3935 20130101; G01J 3/46 20130101;
B41J 11/005 20130101; G01J 3/027 20130101; G01J 3/50 20130101; B41J
29/38 20130101; H04N 1/6044 20130101 |
International
Class: |
B41J 29/393 20060101
B41J029/393; G01J 3/46 20060101 G01J003/46; G01J 3/02 20060101
G01J003/02 |
Claims
1. A system comprising: a color sensor to determine color of color
patches printed on a substrate; a substrate support for supporting
the substrate during operation of the color sensor, the substrate
support including: projections extending from a base of the
substrate support and arranged to support the substrate, and
openings to allow deformation of the substrate towards the base; a
distance sensor to measure a distance indicative of a distance
between the color sensor and the substrate; and a controller to:
determine, using the distance measured by the distance sensor, a
location of a given projection of the projections, and determine a
color of a color patch on the substrate at the determined location
of the given projection.
2. The system of claim 1, wherein the distance measured by the
distance sensor is one of an absolute value of the distance between
the color sensor and the substrate or a value from which the
distance between the color sensor and the substrate is
inferred.
3. The system of claim 1, wherein the controller is to cause
printing of color patches on the substrate at selected locations
based on measurements of distances by the distance sensor.
4. The system of claim 1, wherein the controller is to adjust a
color measurement of the color of the color patch at the determined
location, the adjusting based on the distance measured by the
distance measure.
5. The system of claim 1, wherein the projections are part of ribs
extending from the base, and the openings correspond to spacings
provided between adjacent ribs.
6. The system of claim 1, further comprising a test print engine to
print the color patches on the substrate, wherein the test print
engine is to select at least one dimension of a given color patch
of the color patches based on a positioning tolerance of a
substrate positioning system configured to position the substrate
over the substrate support.
7. The system of claim 1, further comprising a substrate
positioning system to position the substrate such that, for each
respective color patch of the color patches, at least a portion of
the respective color patch is positioned over a respective
projection of the projections.
8. The system of claim 7, wherein the substrate positioning system
is to position the substrate based on a spatial configuration of
the respective projection.
9. The system of claim 1, wherein the determining of the color of
the color patch on the substrate at the determined location is
based on an output of the color sensor.
10. A non-transitory computer readable storage medium storing
instructions that upon execution cause a printing system to:
position a substrate on a substrate support including: projections
extending from a base of the substrate support and arranged to
support the substrate, and openings to allow deformation of the
substrate towards the base; receive, from a distance sensor, a
measured distance indicative of a distance between a color sensor
and the substrate; determine, using the measured distance, a
location of a given projection of the projections; and determine a
color of a color patch on the substrate at the determined location
of the given projection.
11. The non-transitory computer readable storage medium of claim
10, wherein determining the color is based on a color measurement
by the color sensor.
12. The non-transitory computer readable storage medium of claim
10, wherein the instructions upon execution cause the printing
system to print color patches on the substrate at selected
locations based on measurements of distances by the distance
sensor.
13. The non-transitory computer readable storage medium of claim
10, wherein the instructions upon execution cause the printing
system to print the color patch on the substrate with a patch
dimension based on dimensions and locations of the projections.
14. The non-transitory computer readable storage medium of claim
10, wherein the instructions upon execution cause the printing
system to perform color calibration of the printing system based on
determined colors of sample portions being over the
projections.
15. The non-transitory computer readable storage medium of claim
10, wherein the instructions upon execution cause the printing
system to adjust a color measurement of the color of the color
patch at the determined location, the adjusting based on the
measured distance.
16. A method comprising: printing a test pattern on a substrate,
the test pattern including a plurality of color patches;
positioning the substrate printed with the test pattern on a
substrate support including projections extending from a base of
the substrate support, the projections arranged to support the
substrate, and openings between the projections to allow
deformation of the substrate towards the support base, receiving,
from a distance sensor, a measured distance indicative of a
distance between a color sensor and the substrate; determining, by
a controller using the measured distance, a location of a given
projection of the projections; and determining, by the controller,
a color of a color patch on the substrate at the determined
location of the given projection.
17. The method of claim 16, wherein determining the color is based
on a color measurement by the color sensor.
18. The method of claim 16, wherein the projections are part of
ribs extending from the base, the openings correspond to spacings
between adjacent ribs.
19. The method of claim 16, wherein printing the test pattern
includes printing the color patches with distances between central
patch portions of adjacent color patches equal to distances between
central portions of adjacent projections.
20. The method of claim 16, wherein the color patches are printed
on the substrate at selected locations based on measurements of
distances by the distance sensor.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. application Ser. No.
14/375,554, filed Jul. 30, 2014, which is a national stage
application under 35 U.S.C. .sctn.371 of PCT/US2012/024090, filed
Feb. 7, 2012, both are hereby incorporated by reference in their
entirety.
BACKGROUND
[0002] The colors produced by color printers can vary as a function
of media type, ink, print heads, temperature, humidity, etc. To
address color variation, color characterization instruments (e.g.,
spectrophotometers) and device characterization profiling tools
(e.g. International Color Consortium (ICC) profiles) for devices
such as printers may be created. Device characterization profiling
facilitates proper color handling.
[0003] In order to create a printer color profile, a printing
system may print a test color pattern. For example, a test color
pattern may be printed including a plurality of color patches
arranged in a predetermined pattern. A color measurement device
(e.g., a spectrophotometer or a colorimeter) may scan the test
color pattern, and the color measurements may be used to create a
profile for the printer that can be used to insure printing colors
in a consistent manner.
[0004] There are a variety of methods for analyzing colors printed
on a substrate. Such methods include, for example, using a
hand-held spectrophotometer including a wheel that contacts the
color patches on the paper. The wheel is for maintaining a desired
spatial relationship between the spectrophotometer and the paper.
As the spectrophotometer is moved, the wheel measures the speed and
direction of the movement while the spectrophotometer determines
color on locations across the substrate.
[0005] In some other methods, a color sensor (e.g., a
spectrophotometer or a colorimeter) is mounted in the paper path of
the moving sheets in a printer to provide color measurements of the
test color patches printed on the sheets as they pass the color
measurement device. In such color analysis methods, the color
sensor does not contact the paper. However, color sensors may be
sensitive to sensor-to-substrate distance. Hence, factors such as
variations in a paper's position or differences in media thickness
may reduce color analysis accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] In order that the present disclosure may be well understood,
various examples will now be described with reference to the
following drawings.
[0007] FIG. 1A schematically depicts a printing system according to
examples.
[0008] FIG. 1B schematically depicts a front-view of an example of
substrate support for the printing system depicted in FIG. 1A.
[0009] FIG. 1C schematically depicts a partial perspective view of
an example of the substrate support depicted in FIG. 1A.
[0010] FIG. 2 schematically depicts a partial top view of a
substrate support of a printing system according to examples.
[0011] FIG. 3 is a block diagram of a printing system according to
examples.
[0012] FIG. 4 schematically depicts a system according to
examples.
[0013] FIG. 5 is a block diagram depicting a computer readable
medium according to examples.
[0014] FIG. 6A schematically depicts a substrate printed with color
patches according to examples, the substrate being supported by a
substrate support.
[0015] FIG. 6B schematically depicts a substrate printed with color
patches according to examples, the substrate being supported by a
substrate support.
[0016] FIG. 7 is a flow diagram illustrating examples of color
analysis.
[0017] FIG. 8 schematically depicts an arrangement for determining
color on a substrate.
[0018] FIG. 9 shows a graph illustrating color measurements.
[0019] FIG. 10 shows a graph illustrating color measurements.
DETAILED DESCRIPTION
[0020] In the following, numerous details are set forth to provide
an understanding of the examples disclosed herein. However, it will
be understood that the examples may be practiced without these
details. Further, in the following detailed description, reference
is made to the accompanying figures, in which various examples are
shown by way of illustration. In this regard, directional
terminology, such as "top," "bottom," "front," "back," "left,"
"right," "vertical," etc., is used with reference to the
orientation of the figures being described. Because disclosed
components can be positioned in a number of different orientations,
the directional terminology is used for purposes of illustration
and is in no way limiting. Like numerals are used for like and
corresponding parts of the various figures. While a limited number
of examples are illustrated, it will be understood that there are
numerous modifications and variations therefrom.
[0021] As set forth above, there are a variety of methods for
analyzing colors printed on a substrate. However, color analysis
may still be insufficiently accurate for some specific
applications. For example, in methods in which hand-held
spectrophotometers are used, since the spectrophotometer device
contacts the paper, it can distort a color test pattern thereby
making a color measurement inaccurate. Further, in a method using a
color sensor such as a spectrophotometer or colorimeter, since the
color sensor does not contact the paper and color sensors may be
sensitive to sensor-to-substrate distance, variations in a
substrate vertical position may reduce accuracy of the color
analysis. Such differences in the vertical position between
locations of a substrate are referred herein as substrate-height
variability.
[0022] Further, as the present inventors have understood, some
specific printing systems may be particularly prone to
substrate-height variability. More specifically, some printing
systems may include a substrate support for supporting the
substrate, at least, in a color measurement zone during operation
of a color sensor for color analysis. The substrate support may
include projections extending from a base of the support and
arranged to support the substrate. A projection of a substrate
support as referred herein refers to a portion raised with respect
to a support base and providing the contact surface for supporting
the substrate portion during, at least, color analysis.
[0023] The substrate support further may further include spacings
to allow deformation of the substrate towards the support base.
Deformation of the substrate towards the support base may be
desirable in order to avoid upward buckling of the substrate
(upward buckling may damage the substrate and/or printer elements,
such as a printhead, disposed above it). However, as can also be
appreciated from FIGS. 3 and 8, substrate deformation may promote
substrate-height variability. As set forth above, substrate-height
variability may render color measurements performed across a
substrate for color analysis inconsistent.
[0024] Techniques are described herein that facilitate compensating
substrate-height variability influence on color analysis. In some
examples herein, substrate-height variability may be compensated by
conveniently selecting how a color patch is to be printed on the
substrate. More specifically, dimension and location in the
substrate of the color patches may be selected such that, for each
color patch, at least a portion of the color patch can be
positioned on a support projection in the color measurement zone
when the substrate is positioned on the substrate support for
operation of a color sensor. By way of example, the selection may
be performed based on dimension and location of support elements
such as the support projections or openings. Thereby, dimension and
location of color patches may be conveniently selected.
[0025] Further, the substrate may be positioned on the substrate
support such that at least a portion of a color patch printed on
the substrate is on a support projection. Then, color of the color
patch may be determined by operating a color sensor to acquire
color of the color patch at a sample portion of the color patch,
the sample portion being on the support projection. Color
calibration of the printing system may be then based on determined
colors corresponding to sample portions being on support
projections. Thereby, it is facilitated to reduce substrate-height
variability in the color measurements so that color calibration can
be performed using data with better consistency.
[0026] In the following, non-limiting examples of printing systems
that may be particularly prone to substrate-height variability are
illustrated with respect to FIG. 1A-2. FIG. 1A schematically
depicts a printing system 100 according to examples. Printing
system 100 includes a printing arrangement 102 for printing in a
printing zone 103 beneath printing arrangement 102, a substrate 104
while supported by a substrate support 106. A printing arrangement
refers to any arrangement suitable to print a pattern (e.g., a
pattern including one or more color patches) on a substrate. An
example of a printing arrangement is illustrated with respect to
FIG. 3. Examples of color patches are shown in FIGS. 6A, 6B.
[0027] A feeding mechanism 116 may be provided for advancing
substrate 104 towards printing zone 103, i.e., along a media
advance direction 124.
[0028] A test print engine 402 may be communicatively coupled to
printing arrangement 102 for causing printing of a color patch on
substrate 104 as described with respect to FIGS. 4-5. For
performing printing, a printhead of printing arrangement 102 may be
scanned along a transition direction 122 (perpendicular to the
plane of FIG. 1), i.e. across the width of substrate 104 as further
illustrated with respect to FIG. 3.
[0029] In the illustrated example, printing system 100 further
includes a color sensor arrangement 110 for measuring color on
substrate 104 in a color measurement zone 112. For performing color
acquisition, color sensor arrangement 110 may be scanned along
transition direction 122. A color determination engine 404 may be
communicatively coupled to color sensor arrangement 110 for color
analysis as described with respect to FIGS. 4-5.
[0030] In some examples, a printing system may be configured such
that sensor-to-substrate distance with respect to a color sensor
corresponds to a nominal value of the color sensor when color is
acquired at substrate locations positioned over a support
projection. More specifically, height of support projections may be
such that, when the color sensor determines color of a specific
substrate portion on those support projections, sensor-to-substrate
distance corresponds to a nominal value of the color sensor.
[0031] A nominal value of a color sensor is the value, or range of
values, of sensor-to-substrate distance specified by the
manufacturer to operate the color sensor. Vertical distance between
the color sensor and top portions of the substrate support may be
chosen for complying with such nominal values. (Other factors may
be taken into account such as a typical substrate thicknesses or
sensor angle.) A configuration of a printing system for complying
with nominal specifications of the color sensor as described herein
facilitates not only reducing measurement variability but also
improving measurement reliability.
[0032] Herein, printing systems configured as a wet ink printer are
also contemplated. A wet ink printer is configured to use ink
including a relatively high amount of water (e.g. a latex ink). A
wet ink printer may include components for facilitating wet ink
printing and, in view of the relatively high content of water of a
wet ink, for promoting drying of a printed substrate such as
heating systems or pre-treatment arrangements for fixing the ink to
the substrate. In the illustrated example, printing system 100
includes a heat source 116 for heating substrate 104. In the
illustrated example, heat source 116 includes a radiant source 118
(e.g., an infrared lamp). A heat source as referred to herein is
intended to encompass any structure suitable to heat a substrate in
a printing zone. In examples, radiant source 118 may be constituted
by a conductive source (e.g., substrate support 106 may integrate a
heating system for conductively heating substrate 104 such as strip
heater 207 shown in FIG. 2).
[0033] Cooling of print components of printing system 100 (e.g., a
printhead in printing arrangement 102) may be provided by a
fan/blower arrangement 119. For example, fan/blower arrangement 119
may generate a 2 m/s airflow over the surface of the print medium
for cooling of elements in printing arrangement 102.
[0034] Heat source 116 may be configured to heat substrate 104 to a
temperature above 50 degrees Celsius or, more specifically, to a
temperature around 55 to 60 degrees Celsius. In some applications
where it is desirable to cure ink ejected on substrate 104 (e.g., a
latex ink), a further heat source (not shown) may be implemented
for promoting ink curing in a curing zone provided downstream
printing zone 103 by heating substrate 104 to a higher temperature
(e.g., a temperature between 60 and 80 degrees Celsius).
[0035] As an ink contacts a print medium (e.g., substrate 104),
water in the ink may saturate fibers of the used print medium
thereby causing the fibers to expand, which in turn may cause the
print medium to buckle. Buckling, also referred to as cockling, of
a print medium tends to cause the print medium either to
uncontrollably bend downwardly away from the printheads, or to
uncontrollably bend upwardly toward the printheads. In either case,
a constant printhead-to-print medium spacing is not achieved, which
might lead to poor print quality. Additionally, an upwardly
buckling print medium may contact a printhead, which may lead to
ink smearing on the print medium and/or damages in the printhead or
the print medium.
[0036] For addressing substrate buckling, a substrate support may
include openings to allow deformation of the substrate towards a
support base. In the illustrated example, substrate support 106 is
constituted by a platen including (a) ribs 120 extending from a
base 126 of support 106, and (b) openings 121 (show in FIGS. 1B-1C)
formed as clear spacings between adjacent ribs. Ribs as referred to
herein are intended to encompass any set of elongated structure
suitable to support a substrate with spaces provided therebetween.
Ribs may be characterized by any shape such as a non-straight shape
or, more specifically, a zigzag shape. The platen can be flat or
slightly curved, depending on which feed arrangement is used.
[0037] In the illustrated example, conduits 138 (which can also be
appreciated in FIG. 1C) extend through base 126 to openings 121. A
vacuum chamber 128 may be disposed beneath base 126 for maintaining
a vacuum generated by a vacuum arrangement 130. Vacuum arrangement
130 may include a pump system and/or a fan system for vacuum
generation. The vacuum may be further formed into conduits 138 and
openings 121 for (a) holding substrate 104 against upper surfaces
of ribs 120, and (b) further preventing buckling of substrate 104
towards printing arrangement 102.
[0038] Further details on substrate support 106 can be appreciated
from FIGS. 1B-1C. FIG. 1B schematically depicts a front-view of an
example of substrate support 106 for a printing system according to
examples. FIG. 1C schematically depicts a partial top view of
substrate support 106.
[0039] Looking at FIG. 1C, ribs in substrate support 106 extend
generally along straight paths 132 (which can be considered to be
rib axes). Openings 121 in the form of spacings are between
adjacent ribs. Straight paths 132 may be disposed along media
advance direction 124 for facilitating advance of substrate 104 in
that direction. Ribs may include a curved shape or, more
specifically, follow a zigzag path. As shown, the zigzag path may
be smooth rather than angular, e.g., following a waved profile. A
zigzag path as shown in FIG. 1C reduces the length of a contact
surface between the print media and the rib in the media advance
direction, so that the contact across the substrate is distributed
discontinuously in the media advance direction for addressing
imaging artifacts that may result from support contact, as detailed
in U.S. Pat. No. 7,946,700, which is incorporated herein by
reference to the extent in which this document is not inconsistent
with the present disclosure and in particular those parts thereof
describing examples of substrate supports for printing systems.
[0040] To further reduce substrate-rib contact, ribs 120 may be
formed discontinuously. More specifically, each of ribs 120 may
include a running straight base structure 120a and a series of rib
top portions 120b for contacting substrate 104. These rib top
portions 120b define the highest part of substrate support 106, and
act as a discontinuous support surface for substrate 104. Rib top
portions 120b are an example of projections arranged to support a
substrate.
[0041] As will be understood, there are a variety of designs for
substrate supports provided with openings for addressing substrate
buckling. FIG. 2 schematically depicts a partial top view of a
substrate support 200 according to examples. Support 200 includes a
vacuum manifold 201, which may be fabricated of a thermally
non-conductive material. In the example of FIG. 2, openings 221 are
constituted as a plurality of vacuum passageways, or ports,
distributed across a projected surface 204 such that a vacuum can
be draw down through the ports--(the vacuum being represented by
arrows labeled "Fv"). Further, openings 221 are dimensioned for
allowing deformation of the substrate towards the support base.
[0042] Interspersed with the pattern of vacuum ports 203 is a set
of platen surface channels 205. Inlaid within each of the channels
is a strip heater 207 (other patterns and shapes may be employed).
Heaters 207 are connected to a power source (not shown) in any
convenient manner. Strip heaters 207 may implement the
functionality of heat source 118.
[0043] In the example of FIG. 2, projected surfaces 204 as well as
strip heater 207 are examples of projections arranged to support a
substrate. Further examples of substrate supports constituted
similarly as support 200 are illustrated in U.S. Pat. No.
6,454,478, which is incorporated herein by reference to the extent
in which this document is not inconsistent with the present
disclosure and in particular those parts thereof describing
substrate supports for printing systems.
[0044] Openings, such as openings 121-221 described above, prevent
substrate buckling towards a printing arrangement placed over it by
allowing deformation of the substrate towards the base of the
substrate support. Moreover, such openings facilitate ink drying,
which may be particularly important for wet ink printing, and
reduce friction between substrate and support. However, a substrate
support including such spacings may induce substrate-height
variations.
[0045] More specifically, as can be appreciated from FIGS. 3 and 8,
substrate buckles 44 may be formed towards the support base at the
spacings. In these examples, due to the platen ribs, substrate
deformation is directed towards spacings formed between the ribs.
Further, in some printing systems, the substrate is displaced along
the ribs during placement of the substrate on the substrate
support; such a displacement may induce a wave-formed deformation
along the substrate that further promotes buckling forming. In
general buckling formation is difficult to pre-determine.
[0046] A further source for buckle formation may be vacuum
generated by a vacuum system (e.g., vacuum arrangement 130 in FIG.
1A) for improving substrate adherence to the support. The effect of
vacuum on substrate height can be appreciated from FIG. 8: vacuum
45 generated by a vacuum system for improving substrate adherence
to the support may still further promote formation of buckles 44.
By way of example, buckle size (depicted in FIG. 8 by arrow
d.sub.1) may be between 0.5 and 1 mm such as 0.7 mm. Such a buckle
size may be relatively significant when compared to the
sensor-to-substrate distance (depicted in FIG. 8 by arrow d.sub.2),
which may be between 1.2 and 3.7 mm such as 2.7 mm.
[0047] FIG. 3 further illustrates details of a print system
according to examples. FIG. 3 is a block diagram of a printing
system 300 according to examples. Printing system 300 includes a
printing arrangement 102 for printing a pattern (not shown in FIG.
3; some examples are depicted in FIGS. 6A-6B) on substrate 104. In
examples, printing arrangement 102 is configured for inkjet
printing. Printing arrangement 102 may be configured to implement
other printing methods such as laser printing. In the illustrated
example, printing arrangement 102 includes ink printheads 312a-312d
for printing substrate 104 in a printing zone 103. Further,
printing arrangement 102 is provided mounted onto a carriage 316,
which is operatively coupled to a carriage drive 318 for traversing
along transition direction 122. Carriage drive 318 may be
operatively coupled to a position registering system (e.g., a
combination of a servo and an encoder) to facilitate positioning of
the elements mounted on the carriage (e.g., the color sensor).
Printing zone 103 is a region over which printing arrangement 102
can be scanned.
[0048] In the illustrated example, carriage 316 further supports a
color sensor 324. Color sensor 324 is configured to provide a color
output signal associated with color of the printed pattern. The
output signal of color sensor 324 is, generally, sensitive to
sensor-to-substrate distance so that substrate-height variability
may affect the result of a color measurement across substrate 104.
As illustrated, color measurement is performed in a color
measurement zone 112, which is a region over which color sensor 342
can be scanned. Since both color sensor 324 and printing
arrangement 102 are mounted on carriage 316, color measurement zone
112 and printing zone are coincident in the illustrated
example.
[0049] According to some examples, a further sensor 322
(hereinafter referred to as vertical sensor 322) may be included
for providing an output signal associated with vertical position of
substrate locations. Vertical sensor 322 may be a height sensor
that enables determining sensor-to-substrate distance or a more
general sensor that provides an output signal sensitive to
sensor-to-substrate distance. Using a vertical sensor facilitates
compensating substrate-height variability by dynamically selecting
color measurement location taking into account substrate vertical
position so as to reduce color measurement variability across the
sensor scan axis caused by variations in the sensor-to-substrate
distance. Alternatively or in addition thereto, a vertical sensor
may be used for adjusting the output from color sensor 324 for so
as to reduce color measurement variability across the sensor scan
axis caused by variations in the sensor-to-substrate distance. Such
an operation of a vertical sensor is illustrated with respect to
FIG. 7.
[0050] As shown in the Figure, printing system 300 may further
include a substrate support 106 on which substrate 104, or a
portion thereof, lies while color sensor 324 is being operated.
Substrate 104 can be advanced over support 106 in media advance
direction 124, which is perpendicular to the plane of the Figure. A
controller 330 is configured for being operatively connected to the
above elements of Printing system 300 as well as an ink reservoir
332, a memory device 334, and a printjob source 336.
[0051] In the illustrated example, substrate support 106 is
constituted by a platen that includes a base 126 and upstanding and
spaced ribs 342. The ribs illustrated in FIGS. 2 and 6A have a
straight shape along media advance direction 124. As set forth
above, ribs are provided for facilitating substrate displacement as
well as preventing upward buckling of a substrate towards a print
arrangement.
[0052] As used herein, a printhead is a device including nozzle or
nozzles through which drops of a fluid can be ejected towards a
substrate for performing printing. The particular fluid ejection
mechanism within the printhead may take on a variety of different
forms such as, but not limited to, those using piezo-electric or
thermal printhead technology. In the illustrated example, each of
ink printheads 312a-312d is configured to eject ink 338 of a
different color (referred to as base colors). It will be
appreciated that printing system 300 may include any number and
configuration of printheads suitable for a particular
application.
[0053] Ink printheads 312a-312d are fluidly connected to ink
reservoir 332. Ink reservoir 332 includes separated reservoirs
332a-332d for providing ink to the respective ink printhead. In the
illustrated example, reservoirs 332a-332d respectively store cyan
ink, magenta ink, yellow ink, and black ink. Printing systems
commonly employ a plurality of ink printheads to produce secondary
colors by combining ink from different ink printheads. Base colors
are reproduced on substrate 104 by depositing a drop of the
required color onto a dot location. Secondary or shaded colors are
reproduced by depositing drops of different base colors on adjacent
dot locations; the human eye interprets the color mixing as the
secondary color or shading.
[0054] Controller 330 is configured to execute methods described
herein. Controller 330 may be implemented, for example, by one or
more discrete engines and/or modules (e.g., data processing
components) that are not limited to any particular hardware,
firmware, or software (i.e., machine readable instructions)
configuration. More specifically, controller 330 may be configured
to implement any of a test print engine 402, a positioning engine
404, a color determination engine 406, or a color calibration
engine 408, which are illustrated below with respect to FIG. 4.
Controller 330 may be implemented in any computing or data
processing environment including digital electronic circuitry,
e.g., an application-specific integrated circuit, such as a digital
signal processor (DSP) or in computer hardware, firmware, device
driver, or software (i.e., machine readable instructions). In some
implementations, the functionalities of the engines and/or modules
are combined into a single data processing component. In other
versions, the respective functionalities of each of one or more of
the engines and/or modules are performed by a respective set of
multiple data processing components.
[0055] Memory device 334 is accessible by controller 330. Memory
device 334 stores process instructions (e.g., machine-readable
code, such as computer software) for implementing methods executed
by controller 330, as well as data that controller 330 generates or
processes to implement techniques described herein. Memory device
334 may include one or more tangible machine-readable storage
media. Memory devices suitable for embodying these instructions and
data include all forms of computer-readable memory, including, for
example, semiconductor memory devices, such as EPROM, EEPROM, and
flash memory devices, magnetic disks such as internal hard disks
and removable hard disks, magneto-optical disks, and ROM/RAM
devices.
[0056] For printing a pattern on substrate 104, controller 330 may
receive printjob commands and data from printjob source 336, which
may be a computer source or other source of printjobs. Controller
330 typically determines a print mask from the received data. The
print mask may be stored in memory device 334. Controller 330 is
operatively connected to printing arrangement 102 and ink reservoir
332 to control ejection of ink 338 according to the print mask.
Further, controller 330 acts according to the print mask to provide
motion control signals to carriage drive 318 to traverse carriage
316 across substrate 104 (i.e., in transition direction 20).
[0057] Vertical sensor 322 encompasses any type of sensor suitable
to provide an output signal associated with vertical position of
substrate locations. A vertical position refers to a position on
the substrate along an axis perpendicular to the substrate plane
(i.e., a plane corresponding to a non-deformed plane). It will be
understood that substrate vertical position as used herein is with
respect to a substrate portion facing printing arrangement 102.
Further, a substrate location as used herein refers to a substrate
portion facing printing arrangement 102. As used herein, substrate
vertical position is directly correlated to substrate-height.
Substrate vertical position may vary across a substrate due to, for
example, a varying profile of the substrate supports, as
illustrated with respect to FIGS. 1 and 12, or a varying substrate
thickness.
[0058] Each of vertical sensor 322 and color sensor 324 may be
constituted by a plurality of sensors cooperating for performing
the functions described above. Generally, vertical sensor 322 and
color sensor 324 are mounted such that the output of vertical
sensor 322 corresponds to or is indicative of sensor-to-substrate
distance with respect to color sensor 324. More specifically, the
relative spatial configuration between vertical sensor 322 and
color sensor 324 may be such that information associated with the
sensor-to-substrate distance regarding color sensor 324 can be
inferred from the signal output of vertical sensor 322. This
information may enable to (a) directly infer an absolute value of
the sensor-to-substrate distance (see, e.g., the example with
respect to FIG. 2), or (b) infer a parameter correlated to
sensor-to-substrate distance (e.g., the vertical signal output
illustrated with respect to FIG. 4). Regarding (b), in some
examples the relative position between vertical sensor 322 and
color sensor 324 is registered so that information related to
sensor-to-substrate distance with respect to color sensor 324 can
be inferred from the output of vertical sensor 322.
[0059] In the example in FIG. 1, vertical sensor 322 and color
sensor 324 are illustrated mounted on carriage 316. In other
examples, vertical sensor 322 and color sensor 324 may be mounted
on another part of a printing system, for example, on an additional
carriage capable of performing scanning over substrate 104.
Vertical sensor 322 and color sensor 324 may be mounted such that
they can move independently from each other (e.g., by providing
each sensor in independently movable carriages).
[0060] As set forth above, color sensor 324 is to provide a color
output signal associated with color of the printed pattern. A color
sensor may be constituted, for example, by a spectrophotometer or a
colorimeter. As set forth above, vertical sensor 322 is to provide
an output signal associated with vertical position of substrate
locations. Vertical sensor 322 may be a distance sensor such as an
ultrasound sensor or an IR sensor arranged with a pre-determined
spatial configuration such that the signal output of the vertical
sensor enables to infer sensor-to-substrate distance of color
sensor 324. For example, as depicted in FIG. 1, vertical sensor 322
may be arranged in the proximity of, or adjacent to, color sensor
324 and to translate conjointly therewith by mounting both sensors
onto carriage 316. In some examples, vertical sensor 322 and color
sensor 324 may be integrated within the same sensor system as
illustrated in US application with publication number
US2010/284009, which is incorporated herein by reference to the
extent in which this document is not inconsistent with the present
disclosure and in particular those parts thereof describing color
measurement.
[0061] FIGS. 4-5 depict various examples of physical and logical
components for implementing various examples. In discussing FIGS.
4-5, reference is made to FIGS. 6A-6B to provide contextual
examples. Implementation, however, is not limited to these
examples.
[0062] FIG. 4 depicts a system 400 for facilitating color analysis.
System 400 may be integrated in a printing system. For example,
system 400 may be implemented using controller 330 and memory
device 334 depicted in FIG. 3. In other examples, system 400 may be
implemented in a computing system communicatively connected to a
printing system for partially or completely performing the
functionality described herein.
[0063] System 400 includes a test print engine 402 and, optionally,
any of a positioning engine 404, a color determination engine 406,
or a color calibration engine 408. Test print engine 402 is
configured to cause printing of color patches on a substrate. Some
examples of color patches printed on a substrate 104 by operation
of test print engine 402 are illustrated with respect to FIGS.
6A-6B.
[0064] FIG. 6A schematically depicts substrate 104 printed with
color patches 602a-602d, according to an example. Substrate 104 is
supported by substrate support 606 including ribs 604. Ribs 604
constitute support projections arranged to support substrate 104.
More specifically, ribs 604 are straight and substantially flat
such that the ribs support substrate 104 continuously along the
whole depicted rib length. In the depicted configuration, the whole
length of ribs 604 under substrate 104 functions as projections
arranged to support the substrate.
[0065] FIG. 6B schematically depicts a substrate 104' printed with
color patches 602a'-602c', according to an example. (Substrate 104
and color patches 602a'-602c' are represented transparent in FIG.
6B for the sake of illustration.) Substrate 104' is supported by
substrate support 106 described above regarding FIGS. 1A-1C.
Support 106 includes ribs 120 with a zigzag shape. Further, ribs
120 include rib top portions 120b that, in the depicted
configuration, function as support projections arranged to support
substrate 104 discontinuously along the length of ribs 120.
[0066] Referring back to FIG. 4, test print engine 402 is
configured to select dimension and location in the substrate of
color patches. Test print engine 402 performs this selection such
that, for each of the color patches, at least a patch portion can
be positioned on a support projection in the color measurement
zone. By way of example, test print engine 402 may perform this
selection based on dimension and location of support elements such
as the support projections or openings so that dimensions and
location of color patches can be conveniently selected. By way of
example, selection may include dynamically computing dimension and
location in the substrate of color patches based on the spatial
configuration of support projections. In another non-limiting
example, selection may include choosing from a pre-defined set of
patch dimensions and/or locations the most convenient set for a
particular type of support projections and/or openings.
[0067] Examples of the result of a selection performed by test
print engine 402 can be appreciated in the examples depicted in
FIGS. 6A-6B. Regarding FIG. 6A, color patches 602a-602d are printed
with dimensions and locations on substrate 104 such that, as
depicted, the color patches (in this example, the whole area of
each color patch) can be positioned on corresponding support
projections, which in this example are constituted by ribs 604.
Regarding FIG. 6B, color patches 602a'-602c' are printed with
dimensions and locations on substrate 104' such that, as depicted,
a portion of each of the color patches can be positioned on a
corresponding support projection, which in this example are
constituted by rib top portions 120b. In some examples, as shown in
FIG. 6A, each of color patches 602a-602d can be completely
positioned on a corresponding support projection. In other
examples, as shown in FIG. 6B, dimension and location of the color
patches are selected such that only a portion of one or all color
patches can be positioned on a support projection.
[0068] Test print engine 402 may be further configured to select
color patch dimension such that a distance between central patch
portions of adjacent color patches positioned in the color
measurement zone for operation of the color sensor corresponds to a
distance between central rib portions of adjacent ribs over which
central patch portions are positioned for operation of the color
sensor. By selecting in this manner central patch portion
distances, it is facilitated that color patches can be conveniently
positioned with respect to the support projections arranged to
support the substrate. The result of such a selection can be
appreciated in the examples in FIGS. 6A-6B.
[0069] Regarding FIG. 6A, patches 602a-602d are located on the
substrate with a distribution corresponding to that of ribs 604.
That is, the distance between central portions of color patches
602a-602d is equal to central portions of ribs 604 and corresponds
to distance D indicated in the Figure. In this specific example,
patches 602a-602d, as well as the support projections (in this
example, ribs 604) are equidistantly distributed along transition
direction 122.
[0070] In other examples, e.g. as in FIG. 6B, distances between
adjacent support projections may be not equidistant; in other
words, patches may be distributed along transition direction 122
with distances between adjacent patches that may differ from each
other. More specifically, in the example of FIG. 6B, since ribs 120
have a zigzag shape and are out of phase with respect to each other
along media advance direction 124, distances between adjacent
support projections, in this case rib top portions 120b, varies
from rib-to-rib. In this specific example, two different distances
D.sub.1, D.sub.2 between rib top portions 120b are shown. Relative
locations of color patches 602a'-602c' is selected corresponding to
the varying distances D.sub.1, D.sub.2.
[0071] Test print engine 402 may be further configured to select
patch location in the substrate such that the center of a first
patch can be aligned over a first support projection available
under the paper, when the printed substrate is on the substrate
support for color analysis. This can be appreciated from the
examples in FIGS. 6A-6B: in the example of FIG. 6A, the rightmost
patch (i.e., patch 602d) can be aligned over the rightmost rib 604.
In the example of FIG. 6B, the rightmost patch (i.e., patch 602e)
can be aligned over the rightmost rib top portion 120b.
[0072] In order to save costs associated with ink usage, it may be
convenient to print a color patch with reduced dimensions. Some
methods for color analysis require a certain patch size for
averaging color measurements over the path surface in order to
compensate for substrate-height variability effects on color
analysis. In contrast thereto, at least some of the examples herein
do not necessarily require performing such an averaging since
substrate-height variability effects may be prevented using a
single measurement in one color patch. More specifically, at least
some of the examples herein facilitate performing color analysis
using a single measurement at a sample portion on the patch at a
conveniently selected substrate height. Therefore, as the present
inventors have understood, reducing patch size in some of the
examples illustrated herein is not necessarily limited by the
requirement of performing multiple color measurements in order to
provide sufficient data for performing an average.
[0073] Therefore, in view of the fact that a single color
measurement performed on conveniently located patches may already
yield a good basis for color analysis, test print engine 402 may be
further configured to select at least one dimension of a color
patch (e.g., width or length) based on a positioning tolerance of a
substrate positioning system (e.g., feeding mechanism 116 in FIG.
1A) configured to position the substrate over the substrate
support. Note that in the other techniques referred to above, this
positioning tolerance may not be the patch size constraint in view
of a minimum patch size necessary for enabling averaging color
values for a single patch. Taking into account substrate
positioning tolerance facilitates avoiding a misplacement of color
patches relative to corresponding projections while keeping printed
patch size small.
[0074] Depending on the particularly used printing system, field of
view of a color sensor that performs color analysis of the color
patch (e.g., color sensor 324) may be the constraint for selecting
reduced patch dimensions. Therefore, according to some examples,
test print engine 402 may be further configured to select at least
one dimension of a color patch (e.g., width or length) based on
field of view of a color sensor configured to perform color
analysis of the color patch.
[0075] For performing the functions described above, test print
engine 402 may access data related to the spatial configuration of
the support projections as well as position of the color
measurement zone. This data may be stored as part of position data
410 in data store 412.
[0076] Positioning engine 404 is configured to position a substrate
printed with color patches such that, for each color patch, at
least a portion of the color patch is positioned over a support
projection in the color measurement zone. More specifically,
positioning may be performed such that a sample portion of a patch
is over a portion of a projection in a color measurement zone
(e.g., measurement zone 112 shown in FIG. 1). A patch sample
portion refers to a portion of a patch onto which color analysis is
to be performed.
[0077] By way of example, referring to FIG. 1, positioning engine
404 may cause feeding mechanism 116 to laterally align a substrate
with support projections. By way of example, positioning engine 404
may operate a feeding mechanism to position the color patches in
color measurement zone 112 such that a color acquisition can be
performed on patch portions that are on a projection. In the
example of FIG. 6A, in view of the straight shape of ribs 604, this
can be performed directly by simply advancing substrate 104 along
direction 124. In the example of FIG. 6A, in view of the irregular
location of rib top portions 120b, this can be performed directly
by advancing substrate 104 along direction 124 until a location is
reached in which at least a portion of each color patch is on top
rib portion 120b.
[0078] Positioning engine 404 may be configured to position the
substrate based on the spatial configuration of the support
projection and the color measurement zone. For example, positioning
engine 404 may access data related to the spatial configuration of
the printed patches and support projections as well as substrate
position and position of the color measurement zone. This data may
be stored as part of position data 410 in data store 412. Using
this data, positioning engine 404 may cause a substrate positioning
system to position the substrate such that at least a portion of a
color patch is disposed on a support projection, as depicted in
FIGS. 6A-6B.
[0079] For performing its function, positioning engine 404 may
position the substrate based on data provided by a positioning
sensor configured to measure substrate position using the substrate
support, or another element of the particularly used printing
system, as reference. By way of example, a line sensor, an example
thereof is implemented in Designjet printers (e.g., Designjet Z
series) of Hewlett-Packard Company (Palo Alto, Calif., US), may be
used as such a positioning sensor. By way of example, positioning
engine 404 may be configured to position the substrate over the
substrate support such that the center of a first patch is aligned
over a first support projection available under the paper. In the
example of FIG. 6A, the rightmost patch (i.e., patch 602d) is
aligned over the rightmost rib 604. In the example of FIG. 6B, the
rightmost patch (i.e., patch 602e) is aligned over the rightmost
rib top portion 120b.
[0080] Referring back to FIG. 4, color determination engine 406 is
configured to operate a color sensor (e.g., color sensor 110
depicted in FIG. 1A) for determining color of a color patch. More
specifically, color determination engine 406 may cause a color
sensor to generate, for each color patch onto which color analysis
is to be performed, a sensor output associated with a sample
portion within the color patch. The sample portion is over a
support projection. FIGS. 6A-6B illustrate such sample portions:
regarding FIG. 6A, sample portions 603a-603d are associated,
respectively, with color patches 602a-602d; sample portions
603a-603d are located within color measurement zone 112 and above a
rib portion acting as support; regarding FIG. 6B, sample portions
603a'-603c' are associated, respectively, with color patches
602a'-602c'; sample portions 603a'-603c' are located within color
measurement zone 112 and above respective rib top portions
120b.
[0081] From the sensor output, color determination engine 406, or
any other suitably configured computing element, may determine
color of the sample portion. Thereby, it is facilitated that color
analysis is performed using color measurements associated with
substrate vertical positions corresponding to support projections.
Further, thereby, it is facilitated consistency of color analysis
with respect to substrate-height variability. Moreover, as set
forth above, support projections may be arranged such that
substrate locations thereon are at sensor-to-substrate distance
corresponding to a nominal value specified for the color
sensor.
[0082] In some other examples, color acquisition engine 504 is
configured to determine color at sample portions on support
projections by (i) causing and/or receiving color measurements
registered with the location of substrate location in which the
color measurements are performed, and (ii) filtering out color
measurements on the basis of location of substrate location such
that color measurements that correspond to sample portions on
support projections are retained.
[0083] Color calibration engine 408 is to perform color calibration
of a printing arrangement. The color calibration may be based on
colors determined by color determination engine 404. Color
calibration using colors acquired at sample portion over a support
projection as described herein prevents that substrate-height
variability affects the calibration results. Color calibration
refers to measuring and/or adjusting color response of a printing
system. Adjustment may be performed such that color response
corresponds to a known state (e.g., a color standard). Color
calibration using a selected substrate location as described herein
prevents that substrate-height variability affects the calibration
results. It will be understood that a variety of color calibration
methods may be used depending on the particular application of the
color analysis. For example, color calibration may include
establishing a known relationship to a standard color space.
[0084] The components described above with respect to FIG. 4 are
implemented as combinations of hardware and programming. Such
components may be implemented in a number of fashions. As depicted
in FIG. 5, the programming may be processor executable instructions
stored on a tangible memory media 500 and the hardware may include
a processor 502 for executing those instructions. Memory 500 can be
said to store program instructions that, when executed by processor
502, implement system 400 of FIG. 4. Memory 500 may be integrated
in the same device as processor 502 or it may be separate but
accessible to that device and processor 502. In an example, memory
500 and processor 502 are implemented in a printing system, such as
printing system 300, namely, as part of memory device 334 and
controller 330. In other examples, memory 500 and processor 502 are
implemented in a computing system communicatively coupled to a
printing system for implementing the functionality described
herein.
[0085] Examples of system 400 can be realized in any
computer-readable media for use by or in connection with an
instruction execution system such as a computer/processor based
system or an ASIC (Application Specific Integrated Circuit) or
other system that can fetch or obtain the logic from
computer-readable media and execute the instructions contained
therein. "Computer-readable media" can be any media that can
contain, store, or maintain programs and data for use by or in
connection with the instruction execution system. Computer readable
media can comprise any one of many physical media such as, for
example, electronic, magnetic, optical, electromagnetic, or
semiconductor media. More specific examples of suitable
computer-readable media include, but are not limited to, a portable
magnetic computer diskette such as floppy diskettes or hard drives,
a random access memory (RAM), a read-only memory (ROM), an erasable
programmable read-only memory, or a portable compact disc.
[0086] In one example, program instructions can be part of an
installation package that can be executed by processor 502 to
implement system 400. In this case, memory 500 may be a portable
medium such as a CD, DVD, or flash drive or a memory maintained by
a server from which the installation package can be downloaded and
installed. In another example, the program instructions may be part
of an application or applications already installed. Here, memory
600 can include integrated memory such as a hard drive.
[0087] In FIG. 5, the executable program instructions stored in
memory 500 are depicted as a test print module 504, a positioning
module 506, a color determination module 508, or a color
calibration module 510. Test print module 504, positioning module
506, color determination module 508, and color calibration module
510 represent program instructions that when executed cause the
implementation of, respectively, test print engine 402, positioning
engine 404, color determination engine 406, and color calibration
engine 408 of FIG. 4.
[0088] FIG. 7 shows a flow diagram 700 that implement examples of a
color analysis method for calibrating a printing system. In
discussing FIG. 7, reference is made to the diagrams of FIGS. 1-6B
to provide contextual examples. Implementation, however, is not
limited to those examples. Reference is also made to FIGS. 8-10.
Again, such references are made simply to provide contextual
examples.
[0089] Referring to FIG. 7, at block 702 data associated with
spatial configuration of elements in a printing system may be
processed. The spatial configuration data may include spatial
configuration of elements of the substrate support such as
dimensions (e.g., length, width), position, and/or shape of
elements of the support such as support projections. The spatial
configuration data may further include spatial configuration of a
color sensor configured to acquire color measurements for the color
analysis. Referring to FIG. 4, test print engine 402 may be
responsible for implementing block 702.
[0090] Processing at block 702 may include, by way of example,
receiving the data from an external system, accessing stored data
(e.g., spatial configuration data stored as part of position data
410 in data store 412, or receiving a user input. In examples,
spatial configuration data may be previously acquired by a printed
system using suitably configured sensors (e.g., a distance sensor
operated over an unloaded substrate support). Processing at block
702 may also include transforming the spatial configuration data
(e.g., changing units, or absolute spatial references) so that the
data can be used to determine the pattern to be printed.
[0091] At block 703, dimension and location in a substrate of color
patches may be selected such that, for each color patch, at least a
portion of the color patch can be positioned on a support
projection in the color measurement zone when the substrate is
positioned on the substrate support for operation of a color
sensor. Data processed at block 702 may be used to implement block
703. For example, position and location of support projections may
be inferred at block 702; from this information, the dimension and
location of color patches can be computed that enable to position
the substrate over the substrate support such that, for each color
patch, at least a portion of the color patch can be positioned on a
support projection in the color measurement zone. This computation
may be performed iteratively. For example, position and location of
a first patch may be computed using as reference a first support
projection (e.g., a support rib); then position and location of a
second patch may be computed using as reference a further support
projection adjacent to the first support projection; these steps
may be repeated until position and location of all patches to be
printed are computed. Referring to FIG. 4, test print engine 402
may be responsible for implementing block 703.
[0092] At block 704, a test pattern may be printed on a substrate
including color patches with dimension and location selected at
block 703. Some examples of test patterns that may result from
block 704 are illustrated with respect to FIGS. 6A-6B. Referring to
FIG. 4, test print engine 402 may be responsible for implementing
block 704.
[0093] At block 706, a substrate with a test pattern printed at
block 704 may be positioned on a substrate support. The substrate
support includes i) projections extending from a base of the
support, the projections arranged to support the substrate, and ii)
openings to allow deformation of the substrate towards the support
base. Some examples of such substrate support are illustrated above
with respect to FIGS. 1A-2. In a more specific example, block 706
may include positioning at least a portion of a color patch over a
support projection taking into account, at least, dimension and
location of the color patch. As set forth above, the test pattern
may be printed by taking into account the spatial configuration of
the substrate support such that patch portions can be positioned on
support projections. The positioning is performed such that, for
each color patch, a sample portion of the color patch is over a
portion of a projection in a color measurement zone. Some examples
of test patterns positioned over a substrate support according to
block 706 are illustrated with respect to FIGS. 6A-6B. Referring to
FIG. 4, positioning engine 404 may be responsible for implementing
block 706.
[0094] At block 708, color of color patches may be determined. For
example, color may be determined at sample portions in a color
measurement zone of the printing system, the sample portion being
over the support projection. Some examples of sample portions are
illustrated with respect to FIGS. 6A, 6B (see sample portions
603a-603d or 603a'-603c'). Further examples of sample portions at
which color measurements may be performed are illustrated in FIG. 8
by arrows 846.
[0095] Block 708 may include causing a color sensor to acquire
color of a color patch at a sample portion that is located over a
support projection. Referring to FIG. 4, color determination engine
406 may be responsible for implementing block 708.
[0096] According to some examples, the color sensor may be
translated over the substrate while acquiring color only at the
sample portions. For example, as illustrated by FIG. 8, color
sensor 24 may be operated to acquire color only at selected
locations 846 while being scanned along a transition direction 122.
In other examples, the color sensor may be translated over the
substrate while acquiring color only at the locations that do not
necessarily overlay with support projections; a color determination
may then include filtering a set of color measurement for
processing color measurements associated with the sample portions
that are over support projections.
[0097] There are a variety of methods for determining the specific
spatial location of sample portions, i.e. the absolute positions at
which color measurements are to be acquired. By way of example,
this specific spatial location may be determined by taking into
account the spatial configuration of the substrate support,
location of the color measurement zone, and location of the color
patches. For example, a printing system may register substrate
location and, from that information, infer positions of patch
portion; using absolute references, patch portions overlapping
support projection and color measurement zone may then inferred
after the substrate is positioned. An encoding system coupled to
color sensor may be then used to position the color sensor for
color acquisition at the sample portions.
[0098] In other examples, the specific spatial location of sample
portions may be determined dynamically. For example, block 708 may
include selecting a color measurement location (i.e., a sample
portion as used herein) based on a distance measurement indicative
of sensor-to-substrate distance of the color sensor. The selection
is performed such that a color measurement location coincides with
a support projection.
[0099] Such a distance measurement may be performed by a further
sensor (e.g., vertical sensor 322) configured for providing an
output signal associated with vertical position of substrate
locations. Such a further sensor may be, for example, a distance
sensor (i.e., a sensor with which a specific substrate vertical
position can be determined) or a sensor that is sensitive to
sensor-to-substrate distance such as a densitometer. The sample
locations may be determined by analyzing, for example, a
substrate-height profile, or a profile of a signal output
correlated to substrate-height to infer the spatial location of
support projections.
[0100] Determining color of a printed pattern at a sample portion
over the support projections facilitates improving color
measurement quality (in particular measurement reliability) as
compared to conventional methods, as illustrated by FIGS. 9-10.
Both Figures are graphs showing ESP CIE-L* measurements across
different substrates lying on a substrate support constituted by a
ribbed platen: curves 902a-902b correspond to an Offset substrate;
curves 904a-904b correspond to a Vynil substrate (Avery MPI 3000).
FIG. 9 shows color curves 902a-904a acquired without considering
whether sample portions are over support projections. In contrast
thereto, FIG. 10 show color curves 902b-904b acquired using sample
portion over support projections. As can be appreciated, color
curves shown in FIG. 10 are characterized by a lower variability as
compared with the color curves in FIG. 9. By way of example, using
sample portion over support projections may facilitate an accurate
color measurement with variability below 2 CIEDelta E1976 (or
Euclidean distance in CIELabspace). This may translate into a
4.times. reduction of measurement variability across printer platen
as compared to other methods.
[0101] According to some examples, block 708 may include adjusting
color measurements using measurements associated with substrate
vertical position of the selected sample locations for compensating
substrate-height variability. Color measurement adjustment
facilitates a further compensation of substrate-height variability,
which may still influence color analysis even when color
measurements are performed at sample portions located over support
projections.
[0102] Generally, color adjustment is performed using a previous
characterization of how color measurements depend on
substrate-height. A variety of methods may be used for adjustment
of the color measurement. For example, an adjustment matrix may be
stored that correlates the following parameters: (a) adjustment
factors; and (b) sensor-to-substrate distances; a determined
substrate-height may be associated with a corresponding
sensor-to-substrate distance; the sensor-to-substrate distance may
be used to identify an adjustment factor using the adjustment
matrix; finally, a color measurement corresponding to the
sensor-to-substrate distance may be adjusted by applying the
adjustment factor.
[0103] Some examples of methods for adjusting color measurements
based on sensor-to-substrate distances are illustrated in US
application with publication number US 2011/0032526, which is
incorporated herein by reference to the extent in which this
document is not inconsistent with the present disclosure and in
particular those parts thereof describing color measurement
adjustment.
[0104] At block 710, color calibration of the printing system used
for printing the test pattern at block 704 may be performed based
on color determined at block. Referring to FIG. 4, color
determination engine 406 may be responsible for implementing block
708. For performing color calibration, color measurements at sample
portions corresponding to different color patches may be used. For
example, one color measurement per color patch may be used. Using
the color determination, the printer system used to print the
pattern may be color calibrated as illustrated above with respect
to FIG. 4.
[0105] Color calibration as described facilitates reducing color
patch size as compared with some other methods in which
substrate-height variability of color measurements is compensated
by (i) measuring color at multiple locations within one color patch
(e.g., 4 samples per patch), and (ii) averaging the multiple color
measurements for the color patch. Acquisition at multiple locations
generally implies a higher patch area. In contrast thereto,
examples herein facilitate reducing substrate-height variability of
color measurements using a single measurement per patch. Further,
these other methods may require N patches for a specific substrate
width W so that multiple measurements per patch and a useful
average can be obtained; in contrast thereto, at least some
examples herein may be performed such that 2N patches fit the same
specific width W. Hence, substrate area (and length) required by at
least some examples herein may require 35% of the substrate area
required by at least some other methods.
[0106] As a further advantage, in at least some examples herein,
the amount of ink and paper spent in printing a test color pattern
can be reduced since patch size can be kept relatively small.
Moreover, thereby the amount of time can be reduced since the time
used to print and measure a test color pattern for color
calibration can be kept relatively low. By way of example, a
calibration target of 64 color patches may take 40 seconds using
substrate selection compared to 2 min 25 sec of some other methods.
As a further remark, at least some examples herein facilitates
performing color calibration using color measurements at the
nominal sensor-to-substrate distance specified for the color
sensor. In contrast thereto, some other methods do not ensure that
color calibration is performed at the nominal sensor-to-substrate
distance specified for the color sensor, thereby, compromising
calibration reliability.
[0107] In the foregoing description, numerous details are set forth
to provide an understanding of the examples disclosed herein.
However, it will be understood that the examples may be practiced
without these details. For example, it will be understood that a
substrate support as used herein is not limited to a ribbed platen.
Further, it will be understood that examples herein are not limited
to wet ink printers. While a limited number of examples have been
disclosed, numerous modifications and variations therefrom are
contemplated. It is intended that the appended claims cover such
modifications and variations. Claims reciting "a" or "an" with
respect to a particular element contemplate incorporation of one or
more such elements, neither requiring nor excluding two or more
such elements. Further, the terms "include" and "comprise" are used
as open-ended transitions.
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